The invention relates to a fresh gas supply device for an internal combustion engine having an exhaust gas turbocharger.
To enhance the charging of internal combustion engines, for example diesel engines, with the aim of increasing torque and power output, various types of boosting systems are known. Exhaust gas turbochargers (ATL) are frequently used; utilizing the residual energy in the exhaust gas of the internal combustion engine in an exhaust gas turbine, they drive a directly coupled turbo-compressor with the mechanical energy generated in the turbine, the air stream thus generated being supplied, with overpressure, to the internal combustion engine.
A known disadvantage of these boosting devices is their sluggish response behavior during acceleration processes. The causes are, firstly, the characteristic curve of continuous-flow machines, that is, of the ATL, which generate only very low charge pressures when there is low gas throughput, and therefore at low engine speeds. A second cause is the fact that increased air charging is available as an increased exhaust gas quantity for driving the ATL only after the four working strokes of a four-stroke engine have been executed, that is, after two engine revolutions, whereby speeding-up of the ATL is additionally retarded.
To eliminate this disadvantage, the ATL is frequently combined with a mechanically driven positive-displacement supercharger or with a smaller ATL specifically adapted to the small exhaust gas flows during the start-up phase. Both solutions require considerable constructional outlay and installation space, especially because the units are arranged directly on the engine as a result of the necessary mechanical drive or the coupling to the exhaust gas system.
In vehicles which are equipped with a compressor and a compressed air storage system for operating an air suspension system and/or a compressed air brake system, there is an opportunity to inject stored compressed air into the internal combustion engine in the acceleration phase, whereby high engine torque and an associated high exhaust gas flow are available in a very short time. After a boost build-up time of a few seconds, the ATL can reach a stable high pressure level. By means of an optimized electronic control system it has been possible to impart very satisfactory operational behavior to such devices, which are also referred to as PBSs (Pneumatic Booster Systems).
FIG. 1 shows schematically an internal combustion engine 1, the exhaust gas line 15 of which for exhaust gas 70 is connected to an exhaust gas turbine 4 of an exhaust gas turbocharger 2. The exhaust gas 70 drives the exhaust gas turbine 4 and is discharged as expanded exhaust gas 71 through an exhaust gas outlet 16. The exhaust gas turbine 4 is coupled to a charge air compressor 3 of the exhaust gas turbocharger 2, for example by way of an exhaust gas turbocharger shaft 5. The charge air compressor 3 compresses fresh air 40 from a fresh air inlet 11 in order to generate compressed charge air 41 for increasing an induction pressure of combustion air 60 in an intake pipe 14 for the internal combustion engine 1. A fresh gas supply device 10, which is arranged between the charge air compressor 3, or a charge air cooler 6 connected downstream thereof in the flow direction, and the intake pipe 14, serves to inject compressed air 51 into the intake pipe 14 of the internal combustion engine 1 in a controlled manner. The compressed air 51 is compressed by a high-pressure compressor 7 from additional air 50 supplied through an air inlet 17 and introduced via a feed line into a compressed air container 8, from which the compressed air 51 is made available to the fresh gas supply device 10 via a compressed air line 19.
A conventional fresh gas supply device 10 is represented schematically in FIG. 2. It is connected by a charge air inlet 12 to the charge air cooler 6, by an outlet 13 to the intake pipe 14 and by a compressed air inlet 29 to the compressed air line 19. A backflow flap 24, which can be swiveled about a flap axis of rotation 25 for closing and opening the connection of the charge air inlet 12 to the outlet 13, is located between the charge air inlet 12 and the outlet 13 in an inlet section 100. In a version described by the application document WO 2006/089779 A1 in relation to a device for supplying fresh air to a turbocharged piston internal combustion engine and a method for operating same, the backflow flap 24 is adjusted by an adjusting device 26, for example an adjusting motor. In addition, the compressed air line 19 is connected to the outlet 13 via a quantity regulating device 9, for example a valve. A control unit (not shown) serves to control the quantity regulating device 9 and the adjusting device 26. In the event of a demand for torque in a “kick down” event, the quantity regulating device 9 supplies compressed air 51 to the outlet 13 through the compressed air inlet 29. Prior to this, the backflow flap 24 is closed, so that the compressed air 51 does not flow into the charge air compressor 3 of the exhaust gas turbocharger 2 via the charge air inlet 12 against the intake direction, but into the intake pipe 14 via the outlet 13. When the compressed air supply ends, the backflow flap 24 is opened again and the quantity regulating device 9 is closed. At this time the pressure of the charge air 41 compressed by the charge air compressor 3 of the exhaust gas turbocharger 2 is again sufficient.
In this case it is regarded as disadvantageous that the PBS requires a relatively large storage volume for compressed air, and requires compressed air at a high pressure level of more than 10 bar. That is approximately four to five times the pressure level required for boosting, and required to keep the storage volume acceptable and to achieve a rapid response of the system. For this purpose, a high-pressure piston compressor with relatively high energy consumption is required to generate the necessary compressed air. When the compressed air is injected into the internal combustion engine and expanded to the charge pressure level, the predominant part of the pressure energy generated is diminished by throttling.
It is therefore an object of the present invention to make available an improved fresh gas supply device.
Accordingly, a fresh gas supply device for an internal combustion engine with an exhaust gas turbocharger includes the following: a charge air inlet for admitting compressed charge air from the exhaust gas turbocharger; an outlet connected to the charge air inlet, this connection being closable by way of at least one backflow flap which can be swiveled about a flap axis of rotation; a compressed air inlet for admitting compressed air to the outlet; and an adjusting device for adjusting the at least one backflow flap. The fresh gas supply device also includes at least one additional turbocharging device having a compressed air turbine and a compressor coupled thereto. The compressed air turbine is arranged upstream of the compressed air inlet in the flow direction of the compressed air, and compressed air can flow through the compressed air turbine. The compressor is configured to aspirate and compress additional charge air from the charge air inlet and to convey compressed additional charge air to the outlet.
With the aid of the additional turbocharging device an energy efficiency of the fresh gas supply device is improved in that excess pressure energy of the compressed air supplied is made usable.
The pressure level of the compressed air required to operate the fresh gas supply device does not need to be increased, and the storage volume required for this compressed air can be reduced.
The additional turbocharging device is driven by the injected compressed air and generates an additional charge air stream. The excess energy of the compressed air is thereby made effective and the required quantity of compressed air and the associated storage volume are considerably reduced.
The energy stored in the compressed air is converted in a compressed air turbine of the additional turbocharging device into mechanical work which is transmitted to a compressor via a common shaft. The compressor therefore generates an additional charge air stream which, together with the partly expanded compressed air from an outlet of the compressed air turbine, makes available the desired charge pressure in the intake pipe of the associated internal combustion engine. Because the pressure level of the exhaust gas turbocharger is lower in this phase, a backflow flap is closed in order to prevent reverse flow. The increased filling of the internal combustion engine and the rise in the speed of the internal combustion engine as a result of increased power cause a sharp rise in the exhaust gas flow, so that after only a few seconds the exhaust gas turbocharger reaches a pressure level sufficiently high that the boost build-up effect of the fresh gas supply device is no longer required, and the device can be switched off and the backflow flap opened.
In a preferred embodiment, the additional turbocharging device may be integrated in a housing of the fresh gas supply device. An advantageously space-saving constructional unit is thereby made possible.
The compressed air turbine and the compressor of the at least one additional turbocharging device are coupled by a shaft. This shaft may extend through a housing of the fresh gas supply device or, in an alternative configuration, may be arranged outside the housing.
The shaft may be mounted rotatably in bearings configured as air bearings. Negligible frictional losses thereby occur in the bearings.
It is especially advantageous if one of the bearings of the shaft, in the form of air bearings, is supplied with the compressed air and another with the compressed additional charge air. In this way an additional air supply for the air bearings can be dispensed with.
The fresh gas supply device may further include a quantity regulating device which has a closed position and any desired number of open positions, in which open positions the quantity regulating device supplies compressed air to the compressed air turbine of the additional turbocharging device. In this way, in conjunction with a suitable control device, especially effective utilization of the energy present in the compressed air can be made possible.
It is further provided that the adjusting device for adjusting the at least one backflow flap is configured in such a way that a completely open position of the at least one backflow flap is associated with a completely closed position of the quantity regulating device. It is therefore ensured that no reaction of the injected compressed air on the exhaust gas turbocharger occurs.
An internal combustion engine having at least one exhaust gas turbocharger, at least one compressed air container and at least one high-pressure compressor has the above-described fresh gas supply device.
The use of such a fresh gas supply device is especially important in heavy commercial vehicles.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.